1. Field of the Invention
The present invention relates to manipulation devices, and in particular to an industrial robot having a control unit and at least one sensor connected to the control unit through an interface.
2. Description of the Prior Art
The successful use of manipulation devices such as industrial robots depends in large part upon the adaptability of these devices to accommodate different parts and environmental influences. Such industrial robots generally are programmable in a plurality of movement axes and are equipped with grippers (claws) or other tools. Various sensors, such as optical and tactile sensors, are employed for this purpose. The sensors being coupled to the robot and providing signals for influencing the operation thereof. In assembly technology, for example, tactile sensors such as path, force or moment sensors are required in addition to optical sensors for identifying the position of parts to be picked-up and/or transported. The individual assembly operations are monitored with these tactile sensors. In most cases, the signals of the sensors are classified for this purpose, that is, the signals are compared to specific thresholds. If, for example, a bushing is to be pressed by a robot onto a shaft, two thresholds are employed which divide the overall signal range of a force sensor, for example, into three signal ranges which are utilized for the assembly operation. If the sensed force exceeds an upper threshold, for example, an error may exist in that too little play exists between the bushing and the shaft, or the bushing may be canted. If the sensed force is in the mid-range between the upper threshold and a lower threshold, a properly executed assembly step is assumed. If the sensed force falls below the lower threshold, an error arises which may be attributed to too little play between the bushing and the shaft, or to the absence of a bushing. The significance of the signal received from a sensor is thus dependent upon the point in time of the sampling during an event, which requires corresponding processing to be undertaken and the program execution.
Most conventional industrial robots have a control means with simple branch or interrupt instructions, with the status of binary input signals or signal combinations being the deciding factor. Accordingly, sensors are generally employed which enable simple binary decisions such as, for example, reports concerning the presence or completeness of a work piece, or the attainment of a prescribed position. Such thresholds are constant as a result of the mechanical construction or as a result of rigidly prescribed comparison values. Such binary decisions, however, are inadequate for complex assembly tasks because adaptation to changed conditions is not possible.
Industrial robots are also known wherein the signals in digital form of individual sensors are directly supplied to the control means, and are classified when processed in the program run in order to achieve the required statements. The control means required for this purpose, however, are complicated in structure and are often too costly for economical employment of industrial robots in an assembly sequence.
The use of optical sensors for position detection in the context of industrial robots for automatic assembly is described in the periodical "VDI Nachrichten," Number 52, Dec. 26, 1980 at page 13. These optical sensors are directly connected to the control means through a special interface. Programming of the optical sensors is simplified by the use of menus which are shown on a monitor and which are selected. Various parameters may also be defined by means of a light pen. Transfer of this technology for optical sensors to sensors such as tactile sensors, ultrasound sensors or other types of sensors having an analog output is, however, not possible.